Bone regeneration is of enormous importance, particularly in the oral and craniofacial region. Trauma, including surgical removal of tumors in the oral and maxillofacial region, causes bone damage and injury. Congenital disorders may carry severe tissue defects that interfere with normal function and are often disfiguring. The ultimate therapeutic goal for these diseases is regeneration of the tissues to a normal or pre-disease state. Our long-range goal is to determine the cellular and molecular mechanisms involved in the regeneration of dental and craniofacial tissues and to further the development of products for skeletal regeneration and tissue engineering. The objectives of this application are to determine the source and potential of adult stem cells in tissue regeneration and to elucidate the roles of osterix (Osx), a critical osteogenic transcription factor, in the differentiation of bone- and dentin-forming cells. The central hypotheses to be tested are that marrow-derived cells are capable of regenerating oral craniofacial tissues and Osx stimulates the normal cascade of bone anabolic behavior. The rationale is based on the evidence that the conversion of marrow-derived non-differentiated mesenchymal stem cells into mature and functional osteo- and odonto-blasts is a crucial step in bone and dentin formation, as well as in regeneration. Aim 1: To determine the differentiation potential and histogenesis of bone marrow stromal cells (BMSCs) in oral craniofacial regeneration. Using a cell-based approach, the genetically labeled BMSCs will be introduced into oral, dental and craniofacial wounds and, for the first time, the cell differentiation, migration, and subsequent bone and dentin formation in a live animal will be documented. Aim 2: To determine, in vivo, the effects and mechanisms of Osx in promoting BMSC differentiation in bone regeneration and tissue engineering. Using a gene-therapy strategy, Osx will specifically target the bone- marrow and/or local-tissue derived cells, and for the first time, the effects of Osx promoting cell differentiation and enhancing osteogenesis and dentinogenesis will be determined in a novel transgenic model. Results derived from these studies in live animals will help identify new sources of cells, which are the most important element and most powerful engine for tissue engineering. These investigations will also provide novel and important insights into bone and tooth tissue formation using a gene-therapy approach, which will certainly benefit the patients who have tissue defects, damages and injuries in mouth as well as craniofacial regions.